Comcast, which is undertaking the project with Liberty Property Trust, said the tower would be "a dedicated home for the company's growing workforce of technologists, engineers and software architects." The facility will also create a media center in the heart of the city by becoming home to the operations of local broadcast television stations NBC 10/WCAU and Telemundo 62/WWSI, according to Comcast.

"This is yet another historic moment for Comcast," Comcast CEO Brian L. Roberts said. "We continue to be proud to call Philadelphia our home, and are thrilled to build a world-class media, technology and innovation center right in the heart of the city … and to create thousands of jobs and further drive economic activity in the region."

Designed by world-renowned architect Lord Norman Foster of Foster + Partners, the glass and stainless steel tower will add a new energetic, dimension to center city.

The 1.517 million rentable square-foot project will include a new Four Seasons hotel and a soaring, block-long lobby with a glass-enclosed indoor plaza accompaniment to Comcast Center's existing outdoor plaza.

The lobby will feature a restaurant, and a new concourse will provide direct connections with SEPTA's Suburban Station, enhancing accessibility and providing new options for commuters.

The mixed-use tower is expected to be the tallest building in the United States outside of New York and Chicago and will be the largest private development project in the history of Pennsylvania.

"This is a very special project," Foster, the architect, said, expounding on his vision for the project. "It is an opportunity to create a unique and sustainable model for mixed-use, high-density development, which uniquely combines spaces for high-tech research and development with restaurants, gardens, fitness facilities and a significant public reception space — a window on Philadelphia.

"At ground level this 'urban room' embraces the city; it opens the building to the public and anchors it as a vital new neighborhood. It also links directly into the below ground public-transport system. Above this, the highly flexible loft-like spaces and studios are designed for a dynamic way of working — an engine for the city's evolution as the kind of leading technology hub presently associated with Silicon Valley."

The project will be owned by a joint venture, 80 percent owned by Comcast and 20 percent by Liberty Property Trust, and managed by Liberty. The project includes an approximately $1.2 billion private investment of which approximately $900 million will be funded by the joint venture and approximately $300 million will be tenant-funded interior improvements.